1. Field of the Invention
The present invention relates to an endoscope apparatus suitable for use in narrow band light observation.
2. Description of the Related Art
Because a medical endoscope is directed to observe inside of a living body, a light source apparatus for illuminating the inside of the body is required. An illumination light generated by the light source apparatus is radiated on an observation target tissue from a distal end portion of an image pickup unit through a light guide inserted through an insertion portion of the endoscope.
As observation using the endoscope, normal light observation which uses visible light such as white light has been widely performed. With a frame-sequential type endoscope apparatus, illumination lights of three colors of R, G and B are sequentially radiated on a tissue inside of a body cavity by allowing a light source of white light to pass through a rotating filter. Then, reflected light images corresponding to the illumination lights of three colors of R, G and B are acquired in time division to generate a color image from each reflected light image for performing normal light observation.
Further, conventionally, various kinds of special light observation which utilize wavelength characteristics of an illumination light have been also performed. For example, International Publication No. 2010/131620 discloses a frame-sequential type image pickup apparatus for performing narrow band light observation as special light observation. In the narrow band light observation, in order to observe a blood vessel at high contrast, by sequentially radiating a blue narrow band light and a green narrow band light on a living tissue while focusing attention on utilization of a light having characteristics of being strongly absorbed to the blood vessel and being strongly reflected and scattered in a mucous membrane surface layer, contrast between capillaries of the mucous membrane surface layer and a wide blood vessel in a deep portion is highlighted.
The invention disclosed in International Publication No. 2010/131620 is configured so that a green narrow band light G and two blue narrow band lights B1 and B2 can be sequentially radiated. Further, in the image pickup apparatus of International Publication No. 2010/131620, narrow band light observation is performed using a narrow band light observation image, created from reflected light images (narrow band images) corresponding to the narrow band lights G, B1 and B2. Still further, in the invention disclosed in International Publication No. 2010/1316120, an addition amount to be used in addition of an image obtained when the narrow band light B1 is radiated and an image obtained when the narrow band light B2 is radiated is determined based on average brightness of the image.